Method and apparatus for the prodduction of music



Dec. '13, 1938. B. F. MIES SNER 2,140,025

METHOD AND APPARATUS FOR THE PRODUCTION 01f MUSI C Filed June 11, 1936 2 Sheets-Sheet 1 5 Z 1 L 0 o M o a 0/ Z/ w on w D 4 m 3 a w 5 J i 1 m n f u 4 2 i II H| H m 6 w W W w INVENTOR Dec. 13, 1938. B. F. MIESSNER 2,140,025

METHOD AND APPARATUS FOR THE PRODUCTION OF MUSIC' I Filed June 11; 1936 2 Sheets-Sheet 2 such translation means and methods. bratcrs into electric oscillations havingthe form 15 Patented Dec. 13, 1938 I 7 2,140,025

UNITED STATES PATENT OFFICE LIETHOD AND APPARATUS FOR THE PROD- DUCTION OF MUSIC Benjamin F. Mieamer, Millbum 'lownship, N. J.

Application June 11, 1936, Serial No. 84,728

18 Claims. 84-1) 0 This invention relates to the production of Figure 3 is alike view in greater detail of a parmusic from the mechanical vibrations of tuned viticular embodiment; and

brators, and more particularly to systems where- Figure 4 is a partly elevational and partly schein said mechanical vibrations are translated into matic view of another embodiment of my inven- 5 electric oscillations and these in turn into soundtion. 5

i. e., wherein mechanico-electric and electric-. It is customary, in musical instruments involvacoustic translations are successively employed. ing mechanico-electric and electro-acousti'e This application is filed as a continuation in part translation, to employ the mechanico-electric of my'co-pending application, Serial No. 705,888, translating device or system to translatethe vifiled January 9, 1934. brations of the vibrators directly into electric os- 10 Such translations as above mentioned are cillations of the vibrational--i. e., low-frequenbroadly well knowmas are also a variety of means cies. According to this invention, however, the and methods for effecting them. An object of this mechanico-electric translating device or system is invention, however, is the provision of improved employed to translate the vibrations of the vi- According to one known mechanico-eiectric of a current of fixed high frequency modulated at translation method which may be termed electhe vibrational frequencies. The oscillations may trostatic", the vibrations of the vibrators are be amplified at will while in this form; are therecaused to vary osclllatorily an electrical capacity, after demodulated or changed into the form of the capacity variations being employed in the currents of the vibrational frequencies; and may 2 production of the electric oscillations. A more then be further amplified at will and finally specific object of my invention is the provision of translated into sound. improved electrostatic translation means and This procedure has many advantages. A simmethods. ple one is that the total amplification of the oscil- In instruments employing mechanico-electric lations may be carried to greater degrees without 25 translations there are frequently controlled qualielaborate amplifier stabilizing devices, since it is tative characteristics of low frequency electric osdivided between amplifiers operating in difierent cillations translated from the mechanical vibrafrequency ranges. Another is that the oscillations; this provides control of the output tone tions as first produced are suitable for applicaquality. An object of my invention is the provition to the input of existing high-gain amplify- 30 sion in instruments of the class described of iming and electro-acoustic translating systems comproved means and methods for controlling output prising in cascade a high frequency amplifier, detone quality. A more particular object of my inmodulator, low frequency amplifier, and loudvention is the provision. of improved means and speaker-i. e., the usual radio receiving set; this methods for controlling the timbre of the output provides a significant economy. Still further ad- 35 tones. vantages esult from the procedure generally and Other objects are the provision of improved from more particular features incident to its opmeans and methods for amplifying the oscillaeration and structure, as hereinafter more fully tions intermediately of the mechanico-electric appears.

40 and electro-acoustic 'translatings; and the pro- In my invention the function of the translat- 40 vision of a multi-vibrator musical instrument by ing apparatus is to modulate a current of fixed which are produced electric oscillations adapted high frequency in accordance with the vibrations to be amplified and translated into sound by an of the vibrators. In the illustrated embodiments amplifying and electro-acoustic translating sysof the invention the translating apparatus is of tem of well known and commonly available type. the electrostatic form above mentioned. In Fig- 45 Other and allied objects will more fully appear ure 1 a simple embodiment is shown.

from the following description and the appended Herein appear strings I, strung for example claims. over triangular bars or bridges 2 between tuning- In the description reference is had to the acand hitch-pins not herein necessary to show. At

companying drawings, of which: least one ofthe bars 2 may be electrically con- 50 Figure l is a view, partly perspective but prinductive, whereby to connect the strings together cipally diagrammatic, of a simple embodiment of and to further circuit portions as hereinafter set my invention; forth. In slight spaced relation to the several Figure 2 is a like view of a slightly more elabostrings is shown an electrode-for example a rate embodiment; narrow, electrically conductive strip 3, which may 66 lite or other insulating strip 4. It will be obvious that a small electrical capacity will exist between the electrode or strip 3 and the thereto adjacent portion of each string l, and that the several such capacities are in parallel and thus form a total capacity from strip to strings; this total capacity may be designated as 5.

The capacity 5 is connected in series with the generator 5 of current of a fixed high frequency. This frequency is intended to be appreciably above the highest frequency to appear in the finally produced music, and is conveniently above the range of human audibility and permissibly or" such high frequencies as are employed as carriers in radio transmission. A series circuit including the capacity 5 and generator 5 is completed through a device I responsive to current in the circuit. This for example may be a resistance, it being appreciated that the voltage thereacross will vary directly in accordance with the current therethrough.

The-vibration of each string may be produced as by striking with a hammer 8; it will of course be complex-4. e., occur at a particular fundamental frequency and harmonics thereof. Although the string is not relied on itself to produce sound, its vibrational omponents just mentioned are of frequencies intended to appear in the finally produced music-4. e., are of audible frequencies.

A normal value of high frequency current is of course caused by the generator 6 to flow in the circuit S--lii. Upon vibration of any of the strings i there will be oscillatorily varied the capacity 5 and hence its reactance and the impedance of the circint 5-6-1. This variation of impedance may be either substantially linear with respect to the vibration of the portion of the vibrating string adjacent to strip 3, or non-linear with respect thereto, depending on the relations between string-to-strip spacings, string vibration amplitudes, etc, and tending particularly with spacings of the order of peak vibration amplitude to non-linearity. To the extent of the non-linearity it will be understood that the impedance value will vary not only at such frequencies as may be present in the string portion vibration, but also at multiples thereof, which will be understood to be harmonically related to the fundamental vibrational frequency of the string. Obviously the high frequency current in the circuit will be alternately increased and decreased, or in other words modulated, at the frequencies of impedance variation of the circuit.

The degree or percentage of modulation will obviously vary with string vibration amplitude. It will also depend on the ratio of average reactance of the capacity 5 to the average total impedance of the circuit 5-8-1, being greater the greater is this ratio. The degree or percentage ofmodulation will further depend on the relation of the actually varied portion of the capacity 5 to the total capacity, being obviously less the greater is the number of strings I. In the usual case even with high string vibration amplitudes the percentage modulation is relatively low; under these conditions the modulation is substantially linear with respect to the impedance variation, and hence in general bears substantially the same relation to string vibra tion as does the impedance variation.

The modulated high frequency current flowing through the resistance I will obviously produce a similarly modulated high frequency voltage conveniently be secured to the top edge of Bakethereacross. Typical further portions of a complete music-producing instrument or system may be connected as by leads 21 across this resistance. Thus there are shown in Figure 1, in cascade, high frequency amplifier l8, potentiometer l9, demodulator 20, potentiometer 2i, low frequency amplifier 22, and loudspeaker 23. The modulated high frequency voltage appearing across the resistance 1 is amplified by amplifier l8, controlled in respect of amplitude by potentiometer I9, and demodulated by demodulator 20 to produce oscillations of the original vibrational fundamental and harmonic frequencies. These oscillations may be controlled in respect of amplitude by potentiometer 2!, amplified by amplifier 22, and translated into sound by loudspeaker 23.

Itis convenient to think of the modulating action of the capacity 5 as the addition, to a steady high frequency current passing therethrough, of slde-bandsi. e., of currents having frequencies which are. the sums and differences of the fixed high frequency and the several component frequencies of impedance variation. A pair of side-bands-i. e., one sum or upper and one difference or lower side-band--will be produced by each different frequency impedance variation component. The term side-frequency current is conveniently used hereinafter to denote one complete such pair of side-bands, each side-frequency current therefore being actually a current of dual frequency. Upon demodulation each different side-frequency current of course produces a different low frequency current, these low frequency currents corresponding in frequency to the original impedance variation components.

Control of the general amplitude of the modulated high frequency current-i. e., of both side-frequency currents and current of fixed high frequency, as by potentiometer I9or control of the degree of modulationi. e., of the general amplitude ratio of side-frequency currents to current of fixed high frequencymay be employed to effect control of output volume from loudspeaker 23. Such control may beconsidered purely quantitative; it affects only the volume of the output sound. There is also pos sible, however, qualitative control of the modulated high frequency current, for the control of output tone quality.

For example, if there be controlled the relative amplitudes of the several side-frequency currents produced by vibration of any single string l and the resulting impedance variations, there will be controlled the relative amplitudes of the individual low frequency currents which are produced upon demodulation and whose frequencies respectively correspond to those of the impedance variation components; this will result in control of timbre of the output tone. Thus considering the impedance variation occasioned by vibration of any string I as comprising a first component identical in frequency with the fundamental frequency of the string, a second component of twice that frequency, a third of three times that frequency, and so on, the corresponding side-frequency currents may respectively be termed first, second, third, etc., and the presently discussed control is intended to vary at will the amplitude relatiomhips between these side-frequency currents.

In providing this control I may employ, for fundamental frequency (e. g., for each string or other vibrator of a multi-vibrator instrument), 75

a plurality of capacities arranged for oscillatory or vibratory variation with a common fundamental frequency but in mutually distinct manners. Occurrence insuch diflerent manners may,

for example, be occurrence with distinct harcapacities and 5" respectively formed by a portion of each string with conductive strip 3',

, and by a distinct portion of each string with conductive strip 3"; the vibratory variations of capacities 5 and 5" will be of different waveform because these capacities are formed with respectively'different portions of each string, of

which the vibrational harmonic structure and waveform is well known to vary along its length. Respectively in series with the capacities 5 and 5" I may employ the generators 6 and 6" generating currents of identical fixed high frequency; and a single resistance I may complete the series circuit for 5'6' and the series circult for 5--6", the voltage appearing across sucresistance 77 being applied as in Figure 1 to ceeding portions of the circuit.

The identity of the fundamental frequencies of the variations of capacities 5' and 5" results in the production by these capacities of two similarly ordered series or groups of side-frequency currents, while the dissimilarity of waveform of the variations results in different amplitude (or amplitude and phase) relations between corresponding side-frequency currents in the two groups. It will further be appreciated that the two groups of side-frequency currents join in resistance I to form a final combiation. In this final combination the first side-frequency current will be algebraic sum of the first side-frequency currents in the two groups; the second side-frequency current will be algebraic sum of the second side-frequency currents in the twogroups, etc. If the amplitude and/or phase of the composite group of side-frequency currents produced by one of the capacities 5' and 5" be varied-or in other words if the relative amplitudes and/or phases of the two groups of sidefrequency currents be varied-the relative amplitudes of the several side-frequency currents in the final combination will be varied.

I may vary the relative amplitudes and phases of the side-frequency currents produced by the two capacities 5' and 5" by varying the relative amplitudes and phases of the fixed high frequency currents passing therethrough, it being well understood that the amplitude and phase of any side-band for given modulation follow those of the current being modulated. Thus in Figure 2 the arrow through each of the generators 6 and 6" denotes variability of amplitude and phase.

. The oscillatory variations of a plurality of capacities, each caused by a respective complex vibration, may occur in mutually distinct manners, although in the respective vibrations the harmonic structures are identical and the vibrational waveforms similar except for mutual inversion or phase displacement. The oscillations produced by capacities varying in manners which are distinguished from each other only by such vibration phase displacement or inversion are yet adapted for combinationto producea variety of tonal effects, in view of nonlinearities of capacity and impedance variations with the vibranally secured to a respective suitable apertured' reed-block I02 and adapted for selective vibration by an individual flow of air in well known manner; this vibration of each reed will be understood to be in general greatest at the free reed extremity mm, and, as illustrated, to take place in an up-and-down direction. Above each reed, preferably near its free extremity, may be adjustably seemed an electrode or screw I03, as in the stationary insulating block I04; and below the reed, for example opposite the electrode I03, may be similarly secured in stationary insulating block I04" another electrode I93". Each of these electrodes will of course be 50 adjusted as not to be touched by the reed in its vibration, but may typically be adjusted to meet this specification with only a small safety factor. There may also be provided for each vibrator a third electrode I031", for example in very slight spaced relationship to the free end of the reed and most closely approached by the reed at some intermediate point in its. vibrational swing--e. g, at the rest position of the reed. The several vibrators may be mutually connected; corresponding electrodes for the several. reeds may be mutually connected; and the parallel capacities of vibrators to top electrodes I03 may be considered as a single capacity I05, the paralleled capacities of vibrators to bottom electrodes I03" as a single capacity I05, and the paralleled capacities of vibrators to end electrodes I03 as a single capacity I05". In series with each of these three capacities I05, I05" and I05" may be connected a respective one of the generators 6', 6 and 6 of common fixed high frequencyoscillations,. but of independently variable amplitude and phase; and, as in Figure 2, a single common impedance or resistance 1 may complete the three series circuits thus formed.

It is readily seen that the inherently complex vibration of any of the reeds oppositely affects the capacities I05 and I05", so that each capacity is actually varied by a respective complex vibration'having a waveform inverted from that of the vibration varying the other capacity. Accordingly, in view of non-linearities hereinabove mentioned, the capacities I 05' and I05" produce distinct oscillatory impedance variations, and accordingly different composite groups. of sidefrequency currents in the high frequency oscillations passing therethrough. By the variability of the amplitude and phase of the outputs of the generators, 6' and 6 as in Figure there may be combined in the impedance I a wide variety of final side-frequency current groupings. This variety may of course be further widened by the employment of the illustrated capacities I05"; each of these will be increased to a maximum twice per fundamental cycle by the then passage of its ree'd closest to the associated electrode I 03" and will therefore have small fundamental and large double-frequency components, obviously producing a thoroughly distinct composite group of side-frequency components for reguill lable combination with thosefroxn capacities I05 and H15", above discussed.

Figures 2 and 4 are of course relatively schematic; a more specific embodiment of the system of Figure 2, for example, appears as Figure 3. In this figure the generators 6' and 6" of Figure 2 appear as the coils ii and ii", each variably coupled to the fixed coil in and this in turn supplied with current of fixed high frequency by connection thereof through potentiometer 28 to the output of amplifier l8, of which the input is connected to a source l5 of current of such frequency. Preferably the coupling etiicient of each of the coils ii and ii to the coil iii is variable from a, given positive value through zero to a like negative value, as by roof the coil about an associated pivot ll, so ii any voltage within a range of amplitudes .nd ..1 either of two phases may be induced in 1' coil ii and El". There is included in 3 a, coil i' similar to coils ii and it", and a third capacity 5" formed by a conductive strip 3" with the strings; this, as did Figure 4, illustrates the contemplation by my invention of a larger number of translating devices than two, it being obvious that the principles of operation are applicable to any number of translating devices. Shielding schematically shown as 30 may be disposed about the source l5, coils [0, H, H" and H', resistance 7 and at least partially about the strips 3, 3" and 3", for the reduction of sensitivity of the system to stray electrostatic fields; this shielding may be established for example at the potential of strings I.

It is to be observed that the variation in the phases and amplitudes of side-frequency currents produced by each of the capacities 5, 5", 5 is effected by, and therefore necessarily accompanied by, a like variation of the high frequency current flowing through each of the capacities. Thus under certain conditions of adjustment the steady high frequency current through the several capacities may be of low or zero algebraic total in the resistance 1; then the oscillations of fixed high frequency applied to the demodulator later in the circuit would be low or zero, although the side-frequency oscillations were of finite amplitudes. Under these conditions the demodulator would not function properly, it being well recognized that both the fixed high frequency oscillations and side-frequency oscillations are required for proper demodulation. In order to overcome this difiiculty I may abstract an unmodulated voltage of the fixed high frequency from the generating system and add it to the voltage which appears across the resistance 1 and which is fed to the demodulator. Such a voltage may be obtained from a coil shown in Figure 3 as coil 24, coupled to the coil I0, and connected in series with one of the leads 21. In order that this voltage may always be made to increase and not further to decrease the steady high frequency voltage appearing across resistance 1 I may make the coupling of the coil 24 to coil in variable, as is the coupling of each of the coils H, H", il, so that phase may be reversed, as well as amplitude controlled, at will.

Instead of relying on frequent adjustments of coil 24, however, I prefer to arrange the circuit so that the unmodulated voltage under discussion will be positively maintained in a phase somewhere near 90 degrees removed, either forward or backward, from the phase of the steady high frequency voltage across resistance 1. This is readily accomplished by inserting an inductance coil 25 in series with coil 24, and a resistance 26 across both coil 24 and inductance 25, so apportioning the ratio of absolute reactance value of inductance 25 (at the fixed high frequency) to the value of resistance 25 as to satisfy the desired phase conditions. Thus letting R representthe normal value of resistance 1 and X the absolute 'reactance value of all the capacities 5, 5" and 5". considered in parallel, the mentioned ratio should be fixed at R/ X.

In Figure 3 the leads 2'! are shown connected to the input circuit of c. thermionic amplifying tube iBa, which is analogous to a portion of the high frequency amplifier l8 in Figure 1. The cathode of this tube may be heated by any suitable means, not shown; its grid may be biased negatively with res; cci; to the cathode as by battery 3i; and its an de current me" be supplied as by battery 32. The current transmitted from tube 18a to further circuit portions need oi" course compri e only frequencies lying in the hand between the fixed high frequency less the highest modulating frequency and the fixed high frequency plus the highest modulating frequency. For highest transmission efficiency within this band the output circuit of the tube l8a may be tuned, as by the capacity 33 and indutcance 34.

Figure 3 illustrates the principal high frequency amplification, the demodulation, and the low frequency amplification as performed by a radio receiver 29, to the output of which is connected or in which is in included the loudspeaker 23. The input of the receiver 29 is connected through the leads 35, which may be shielded as .by an extension 3| of the shielding 30, to the coil 36 coupled to the inductance 34. The radio receiver is, of course, to be tuned to the fixed high frequency, which is therefore chosen to be within its tuning range. The volume control or controls of the radio receiver 29-analogous to II and 2| of Figure 1--may of course be employed to control the level of output sound from loudspeaker 23.

, It may be more convenient, however, to control this output sound level in other portions of the system. In the ordinary case this may be done by varying the amplitude of the side-frequency currents and preferably of the current of fixed high frequency as well; this may be done by adjustment of potentiometer 2|. In the special case, however, in which the radio receiver 28 is of the type which automatically reduces the amplifying action of its high frequency amplifying portion as the amplitude of oscillations therethrough increases, there will be found generally ineffective an attempted control of output volume level in the manner just outlined as preferred for the simple case. In this special case, control of output volume by adjustments of system portions preceding the receiver 2! may be effected by control of the effective percentage modulation as seen by the receiver. A specific manner of effecting such control is to vary the fixed high frequency oscillation amplitude at the tube I84 without change of amplitude of the sidefrequency oscillations; this may be done as by adjustment of the coupling of coil 24 to coil II. It is to be noted that increase of this fixed high frequency oscillation amplitude will decrease the output volume, and vice versa.

Control of qualitative characteristics of the modulated current is not limited to variation of relative amplitudes of the several side-frequency currents therein for timbre control purposes. In

with said vibrator and being adapted to moduvarious United States Letters Patent heretofore issued to me--i. e.. No. 1,912,293, May 30, 1933;

No. 1,915,858, June 27, 1933; No. 1,933,295, 06150-- ber 31, 1933; and No. 1,933,298, October 31, 1933- I have shown various special arrangements of vibrators and of translating devices with respect thereto, for the control of the successive instantaneous amplitudes, or dynamic characteristics, of the output tones. It will be obvious that the translating devices, when employed according to the instant invention for the modulation of a fixed high frequency instead of the direct production of a low frequency current, are still entirely susceptible of arrangement in the manners disclosed in those patents for the production of effects similar to those set forth herein.

The regulable translation from a vibrator by means of a plurality of devices (e. g., electrodes) arranged in association with substantially a single portion of the vibrator (e. g., arranged above and below, and if desired opposite, a single reed portion) isnot in itself broadly claimed herein; broad claims thereto have been made in my copending application #758,155, filed December 14, 1934.

While I have disclosed my invention in terms ofparticular embodiments thereof, it will be understood that these embodiments are illustrative rather than comprehensive, and that the scope of my invention is intended to be expressed in the following claims.

I claim:--

1. In a musical instrument, the combination of a tuned vibrator; a source of high frequency electric oscillations; and a mechanico-electric translating device and means for supplying said oscillations thereto, said device being associated with said vibrator and being adapted to modulate said oscillations in accordance with the vibrations of said vibrator.

2. The combination claimed in claim 1, further including means for adding to said modulated oscillations unmodulated oscillations of said high frequency, and means for controlling the amplitude of said added oscillations.

3. The combination claimed in claim 1, further including means for adding to said modulated oscillations unmodulated oscillations of said high frequency, and means for displacing the phase of said added oscillations.

4. In a musical instrument, the combination of a tuned vibrator; a conductive element in spaced relation thereto and forming therewith an electrical capacity adapted to be oscillatorily varied by the vibration of said vibrator; and a circuit serially including a source of high frequency oscillations, a current-responsive device,

and said capacity.

5. In a musical instrument, the combination of a tuned vibrator; a source of high frequency electric oscillations; mechanico-electric translating means and means for supplying said 05-. cillations thereto, said translating means being associated with said vibrator and being adapted to modulate said oscillations in accordance with the vibrations of said vibrator; and means for. controlling qualitative characteristics of the modulated oscillations.-

6. In a musical instrument, the combination of a tuned vibrator whose vibration includes a plurality of harmonically related audible frequency components; a source of high frequency oscillations; mechanico electric translating means and means for supplying said oscillations thereto, said translating means being associated late said oscillations in accordance with the vibrations of said vibrator whereby said oscilla-' tions are caused to include side-frequency components respectively corresponding to said vibration components; and means for controlling the relationships between the several side-frequency components of the modulated oscillations;

7. In a musical instrument, the combination of a tuned vibrator; a plurality of mechanico-electric translating devices and means for supplying thereto respectively a plurality of currents of a common high frequency, said devices being variously associated with said vibrator whereby to modulate said currents in respectively difierent manners; and means connectedwith said translating devices for combining the modulated currents therefrom to produce a composite modulated current.

8. The combination claimed in claim 7, further including means associated with said supplying means for varying the relationships between the several said currents.

9. The combination claimed in claim 7, further including means for varying the relationships between the several said currents.

10. The combination claimed in claim '7, further including means for adding to said composite current an unmodulated current of said high frequency 11. The combination claimed in claim 7, further including means for adding to said compositecurrent an unmodulated current of said high frequency, and means for displacing the phase of said added current.

12. In a musical instrument, the combination. of a tuned vibrator; a plurality of electrodes varof mechanico-electric translating devices and means for supplying thereto respectively a plurality of currents of a common high frequency,

said devices being associated with respectively different portions of said vibrator, and respectively adapted to modulate said currents in accordance with the vibrations of the therewith associated vibrator portions; and means connected with the several said translating devices for combinig the modulated currents therefrom to produce a composite modulated current.

14. In a musical instrument, the combination of a tuned vibrator different portions of which vibrate at the same fundamental frequency but with different waveforms; a plurality of me chanico-electric translating devices'variously associated with said vibrator and arranged to modulate in respectively different manners high frequency oscillations thereto supplied; a source of oscillations of fixed high frequency; a plurality of coils coupled to said source, the coupling thereto of at least one of said coils being variable; a plurality of circuits, each including a respective one of saidcoils and a respective one of said sponsive means connected with all of said circuits.

15. A musical instrument having output terminals adapted for connection to the input of a radio receiver, comprising in combination a plurality of tuned vibrators and means selective with respect thereto for vibrating the same; a mechanico-electric translating system and means for supplying thereto electric oscillations of high frequency, said system beingassociated with said vibrators and adapted to modulate said high frequency oscillations in accordance with the vibrations thereof; and means connected with said translating system for supplying modulated oscillations therefrom to said output terminals.

16. The instrument claimed in claim 15, fur ther including adjustable means for supplying to said output terminals unmodulated oscillations of said high frequency, whereby the effective degree of modulation of said modulated oscillations may be controlled.

17. A musical instrument having output terminals adapted for connection to the input of a radio receiver, comprising in combination a plurality of tuned vibrators and means selective with respect thereto for vibrating the same; a plurality of mechanico-electric translating systranslating devices; and a common current retems and means for supplyingthereto respectively a plurality of currents of a common high frequency, said systems being variously associated with each of said vibrators, and adapted to modulate said high frequency currents in respectively different manners; means for controlling the relationship between the currents modu lated by the several said translating systems; and means for supplying to said output terminals the several said modulated currents.

18. The method of producing a musical tone of given fundamental frequency and of varying its timbre, which includes producing in each of a plurality of currents of common high frequency a complex modulation whose components are of the given frequency and harmonics thereof, the inter-component amplitude ratios in the modulations of the several said currents being respectively different; controlling the relationships between the several said modulated currents; com hining the several said modulated currents to produce a composite modulated current; demodulating'said composite current, whereby to produce a complex current of the given frequency and harmonics thereof; and translating said last mentioned complex current into sound.

BENJAIVHN F. MIESSNER. 

